1. Field of the Invention
The present invention relates generally to a method and apparatus for eliminating deleterious pathogens from household drinking water, and more particularly to a method and apparatus for infusing ozone into drinking water in order to purify and disinfect the water.
2. Discussion of the Prior Art
Household drinking water dispensing systems have a long history of usage. Although local water utility districts provide customers with potable drinking water, many residential water users desire to either purchase their own drinking water in place of utility-supplied water, or to provide additional treatment to utility-supplied, residential drinking water at the point of the water's use.
A residential water user's objective for either substituting or additionally treating utility-supplied drinking water is to achieve truly "clean and pure" drinking water; i.e., drinking water which is free from those heavy metals, sediments, chemicals, contaminants, pathogens, and other impurities that either cannot be or are not removed by the local water utility. Various commercial enterprises have been formed to meet this consumer demand for "clean and pure" drinking water.
One common type of residential drinking water system is the five-gallon glass or plastic water bottle which sits on a dispensing stand in the home or office. Full five-gallon water bottles are delivered to a residence (or private business) on a regular basis and exchanged for empty bottles. The commercial enterprises which provide such bottled water service to their customers make various representations regarding the water's purity and cleanliness. The water dispensing systems generally chill the drinking water, and may also have the capability to provide heated water for hot beverages.
Another common type of residential system provides supplemental treatment of water at the water's point-of-use. by filtering or purifying the drinking water within the drinking water dispensing system itself.
Another common type of water dispensing system includes an ultraviolet filter utilizing an ultraviolet lamp housed inside a glass chamber. Drinking water flows past the glass chamber as the water is being dispensed, but the water does not come in contact with the ultraviolet lamp nor is there any residual contact time between the water and the ultraviolet light. Thus, in such systems the contact time for, purposes of disinfecting the water by irradiated ultraviolet light is limited to the rate of the water flow past the lamp. Furthermore, the quartz glass of the ultraviolet light bulb is slowly solarized by the high intensity ultraviolet light. This process inevitably darkens the quartz glass, and eventually the amount of ultraviolet irradiation decreases with time. Typically, a 30-percent annual reduction in ultraviolet light intensity is observed.
Ozone injection is another commonly used method for purifying water. Ozone is commonly used as a bacteriostat in water treatment plants. It is well recognized that ozone is capable of producing the high purity, sterile water required by the pharmaceutical industry to manufacture pharmaceutical products and by the semiconductor industry to manufacture circuit boards. Almost all commercial bottled water is purified with ozone. The hotel industry utilizes ozone generators to purify recirculated air in hotel rooms. Ozone has been shown not only to destroy all bacteria completely, but also to destroy virus, spores, and cysts while it removes dissolved organic materials by oxidative processes.
Chlorine treats water much slower than ozone because it must first diffuse through the cell wall of the bacterium. Thus, contact time for chlorine eliminating a microbe can be 10-55 times longer than with ozone. Tests have shown that the rate or speed of E. coli kill by ozone is up to 3,000 times faster than chlorine. Cryptosporidium oocysts resist chlorinating. Disinfecting of C. parvum oocysts with chlorine at typical treatment concentrations has almost no effect, even after several hours contact time. Ozone, on the other hand, is the most effective disinfectant against C. Parvum oocysts. Ozone can completely inactivate the oocysts. Legionella is a danger when it enters the water supply distribution system because they are not killed by the usual chlorine dosage mandated for municipal disinfection.
Ozone does not produce harmful fumes, will not explode, and will not damage plumbing fittings or pipes. Ozone does not leave any chemical taste or smell. Adding ozone to household drinking water adds no contaminants or by-products to the water. Ozone is a chemical-free water treatment method that utilizes the same electrical process produced by lightning as it literally purifies the atmosphere during an electrical storm. In fact, the recognizable scent associated with a rainstorm is a result of the production of ozone in the lower atmosphere. Ozone can destroy microorganisms in water, including bacteria and viruses like Escherichia coli (E. coli), Cryptosporidium, Poliovirus, Giardia muris, and Giardia lamblia. Ozone also removes inorganic compounds, such as iron, hydrogen sulfide, and other contaminants from water.
In addition to providing purification of utility-supplied drinking water, ozone can solve most common well water problems caused by organic and inorganic compounds, including; rust or back colored water; stained clothes or fixtures; discolored, unpalatable food and beverages; slime in toilet tanks and sinks; fuzzy particles in water; smelly or cloudy water; and algae.
Ozone is a low molecular weight molecule composed of three oxygen atoms arranged in a chain. Ozone is an allotrope of oxygen, meaning it is composed of the same atoms but they are combined in a different way. Ozone is activated oxygen; i.e., the 3-atom molecule of ozone is not completely stable--it has too many atoms clinging together. Oxygen is most stable when it is only a 2-atom molecule.
In water, ozone will change back to oxygen in normal course in approximately 20 minutes. However, because of its inherent instability, any time ozone comes into contact with a different kind of molecule, like an inorganic metal (iron or manganese), or an organic molecule (bacteria or virus), the ozone molecule pulls some electrical energy away from the so-called "host" molecule. This process is called oxidation. When ozone pulls away electrical energy from a host molecule, two things happen. First, the excess energy separates one of the three oxygen atoms from the ozone molecule, leaving a stable oxygen molecule and a very unstable oxygen atom. At the same time, the host molecule that lost some of its energy wants to get that energy back. It does so by pulling in the severed oxygen atom to fill in the empty space. If it is an inorganic metal molecule, the added oxygen atom turns it into a metal oxide. If it is an organic molecule, the added oxygen atom changes the electrical bond holding the molecule together, which makes the whole molecule come apart. Bacteria and virus cells literally split apart and dissolve when they absorb an oxygen atom that has been severed from a molecule of ozone.
Bacteria are killed by ozone via rupture of the cellular membrane. This process, known as cell lysing, results in the cellular cytoplasm being dispersed in the water. Under conditions of cell lysing, reactivation of the immobilized bacteria or virus cell is impossible.
Ozone, which is a powerful oxidant, has a high chemical reactivity which arises from its unstable electron configuration that seeks electrons from other molecules. Ozone kills microorganisms by oxidative processes. During its reaction with other molecules, ozone is destroyed and the host is oxidized. The pH of water is not changed when ozone is added. This differs from other oxidizers, such as chlorine, which require the use of caustic or lime to adjust the pH, thus altering overall water quality when by-products are left in the water; for example, when chlorine reacts with the remaining organic compounds in water to from carcinogenic compounds such as the trihalomethanes.
Over a 20-year period of research, ozonation conditions have shown that in normal operation, water containing no suspended and little oxidizable matter is completely free of pathogenic bacteria after ozonation. Ozone is not just a disinfectant, it is in fact a sterilant.
Ozone has a relatively short half life. During the process of water treatment, any unused, or un-oxidized, ozone (O.sub.3) reverts back to oxygen (O.sub.2). Because ozone is a short-lived unstable gas it must be generated at the site of contact by an ozone generator, or ozonator. Contact time between the water and any filtering medium is the most important factor in drinking water purification. In order to optimize the mechanism of cellular destruction, bacteria should be brought into intimate contact with ozone.
Olsen (U.S. Pat. No. 5,683,576, issued Nov. 4, 1997) discloses a water ozonation treatment apparatus including: a chemical treatment tank (CT tank) having a raw water inlet for receiving raw water, an ozone inlet for receiving ozone into the CT tank in order to treat the raw water, and a treated water outlet for providing treated water; an ozone generator and pump for pumping ozone into the CT tank; a water dispensing tank having an inlet for receiving treated water from the treated water outlet of the CT tank, and a water dispensing spout; and means for recirculating water from the water dispensing to the CT tank for re-treatment when required due to recontamination.
One problem with the process taught by Olsen, in which treated water is recirculated from the dispensing tank to the CT tank for re-treatment, is that it is difficult to control the level of ozonation of the water. Overly-ozonated water has a bad taste and is therefore not desirable for human consumption. Under-ozonated water is subject to bacterial infection. Important parameters in controlling the process of ozonation of water include: the time during which the water is injected with ozone; the temperature of the ozonated water which is ideally just below room temperature; and the volume of water being ozonated. By recirculating water from a drinking water tank to a CT tank, it is difficult to track the amount of water in the CT tank which has been previously subjected to ozonation and how much of the water has not been previously subjected to ozonation.
Olsen teaches the use of ozone sensors for detecting the levels of ozone in the CT tank and dispensing tank. A microcontroller is responsive to a first ozone sensor in the dispensing tank and a second ozone sensor in the CT tank. Based on signals received from the ozone sensors, the microcontroller determines: (1) when to recirculate water from the dispensing tank to the CT tank; (2) a specific concentration of ozone in solution to be used in ozonating water in the CT tank; and a time for which the water should be treated. Therefore, in the system taught by Olsen, the level of ozonation in drinking water dispensed from the dispensing tank is dependent upon the accuracy of multiple ozone sensors. Therefore, a complex control process is required for controlling a system which recirculates water from a dispensing tank to a CT tank. The apparatus required for recirculating water, including a pump, is expensive. Also, ozone sensors and control ciruitry responsive the ozone sensors is complex and expensive.
Ozone has a relatively short half life. During the process of water treatment any unused, or unoxidized, ozone (O.sub.3) reverts back to oxygen (O.sub.2).